Nutritional dynamics during embryonic development in the viviparous genus Sebastes and their application to the assessment of reproductive success

Abstract

Concentrations of lipids and protein were measured in embryos during gestation in two species of vi- viparous rockfishes off the central Cali- fornia coast. Total lipids and protein de- clined linearly through embryonic maturation in semipelagic yellowtail rockfish, Sebastes flavidus, and pelagic shortbelly rockfish, Sebastes jordani. Energetically, lipids were the predomi- nant source of energy for embryonic development in both species, but lipid and protein catabolism was signifi- cantly greater for yellowtail rockfish. Total lipids, protein, and lipid class composition were measured during embryonic maturation in three popu- lations of shortbelly rockfish, located at Ascension, Pioneer, and Bodega subma- rine canyons, to determine intraspecific variability of nutritional dynamics. Triacylglycerols and polar lipids (mostly phospholipids), the predominant lipid classes in all maturation stages, were depleted through embryonic develop- ment. Steryl or wax esters and choles- terol also declined, but were in much lower concentrations. The goodness-of- fit of linear regressions for protein, to- tal lipid, and lipid classes by stage of embryonic maturation allowed estima- tions of their concentrations at birth, thus providing a measure of nutritional condition, or qualitative reproductive success. Analyses determined that there were significant differences in metabolism and estimated concentra- tions at birth of nutrients between the two species and among the shortbelly rockfish populations, indicating differ- ential potential for survival during early planktonic life stages until favor- able feeding conditions occur. Results suggest that the contribution of indi- vidual populations to the diversity of metapopulations or year classes may be influenced by the nutritional condition of larvae at birth. (Eldridge and Jarvis, 1995) or other species (Shepherd and Cushing, 1980). Thus, maternal processes contributing to the health or fitness of embryos or early larvae, in addi- tion to the more often assessed en- vironmental factors, may signifi- cantly influence survival and year- class strength. The assessment of reproductive success includes the determination of both the quantity and quality of progeny because year-class strength may be influenced by the health of newborns as well as by the number produced. Although fecundity is of- ten used as a measure of reproduc- tive success and has been related to biological and environmental fac- tors (Blaxter, 1969), less attention has been given to the assessment of the qualitative aspects of repro- ductive success. This is due, in part, to the difficulty of determining which variables or processes are valid measures of egg, embryo, or larval health. Various measures have been proposed, such as egg size (Blaxter and Hempel, 1963), histo- logical criteria (Theilacker, 1978), and biochemical analyses, including nucleic acids (Buckley, 1984), en- zyme activity (Clarke et al., 1992), and biochemical composition (re- viewed by Ferron and Leggett,